The new discovery gives us clues to how fluoride – an element found in our bones and teeth – forms in space. With the help of the Atacama Large Millimeter/submillimeter Array (ALMA) radio observatory, of which the European Southern Observatory (ESO) is a partner, a team of astronomers has discovered this element in a galaxy so far away that light takes 12 billion years to reach us. This is the first time that fluorine has been detected in a galaxy that forms such distant stars.
“We all know fluoride because it’s in the toothpaste we use every day,” explains Maximilian Franco, of the University of Hertfordshire, UK, who led this new study. Published in Nature Astronomy.
Like most elements around us, fluorine forms inside stars, but until now we didn’t know how this element formed. “We didn’t even know what kind of star created the most fluorine in the universe!”
Franco and his colleagues discovered fluoride (in the form of hydrogen fluoride) in massive clouds of gas in the distant galaxy NGP-190387, which we observed when the universe was only 1.4 billion years old, or about 10% of its current age.
Since stars spit out the elements that form in their cores when they reach the end of their lives, this discovery means that stars that formed fluorine must live and die very quickly.
The team believes that Wolf-Rayet stars, extremely massive stars a few million years old and a blink of an eye in the history of the universe, are the places most likely to produce fluorine. Scientists believe these stars are necessary to explain the large amounts of hydrogen fluoride that the team discovered.
Wolf-Right stars have previously been suggested as possible sources of cosmic fluorine, however, until now astronomers did not know how important they were in the production of this element in the early universe.
“We’ve found that Wolf-Rayet stars, who are among the biggest we know and can explode violently when they reach the end of their lives, somehow help us maintain good oral hygiene!” Franco yells playfully.
In addition to these stars, other scenarios have appeared in the past that explain how fluorine is formed and released, such as the pulsation of giant stars that developed with sometimes masses up to our sun, the so-called stars in the asymptotic giant branch. However, the team believes that these scenarios, some of which last for billions of years, may not fully explain the amount of fluorine we see in NGP-190387.
“It took this galaxy a few tens or hundreds of millions of years to obtain fluorine levels similar to those in the stars of the Milky Way, which is 13.5 billion years old. This is a completely unexpected result,” explains Chiaki Kobayashi, a professor at the University of Hertfordshire. “Our measurements set new frontiers on the origin of fluorine, which we have been studying for two decades.”
This discovery at NGP-190387 represents one of the first discoveries of fluorine outside the Milky Way and neighboring galaxies. Astronomers have already discovered this element in distant quasars, bright objects that feed on supermassive black holes at the center of some galaxies. However, until now, fluorine has never been observed in a star-creating galaxy so early in the history of the universe.
The team’s discovery of fluorine was accidental, thanks to the use of observatories installed on the ground and in space. NGP-190387 was originally discovered by the European Space Agency’s Herschel Space Observatory and later observed with ALMA in Chile, which is extremely remarkable for its remoteness.
ALMA data confirmed that the brilliant glow of NGP-190387 was caused in part by another known massive galaxy, located between NGP-190387 and Earth, very close to our field of view. This massive galaxy amplified the light that Franco and his team saw, allowing them to identify the faint radiation emitted by fluorine from NGP-190387 a billion years ago.
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